Silicon silyl

An ether protecting group can be difficult to remove (deprotect). It often requires strong acid, which can react with the free hydroxyl group or other parts of the molecule. Ethers based on silicon (silyl ethers) are much easier to remove than carbon-based ethers. In aqueous or organic solvents, fluoride ion removes silyl ethers under gentle conditions because the silicon-fluorine bond is exceptionally strong. 

Presumably because of the longer bonds to silicon, silyl cations are much more reactive than analogous carbocations. They are extraordinarily powerful Lewis acids and have recently been applied as such to novel synthetic problems. One such application that we have discussed is fluoride ion abstraction. 

The Peterson reaction has two more advantages over the Wittig reaction 1. it is sometimes less vulnerable to sterical hindrance, and 2. groups, which are susceptible to nucleophilic substitution, are not attacked by silylated carbanions. The introduction of a methylene group into a sterically hindered ketone (R.K. Boeckman, Jr., 1973) and the syntheses of olefins with sulfur, selenium, silicon, or tin substituents (D. Seebach, 1973 B.T. Grdbel, 1974, 1977) illustrate useful applications. The reaction is, however, more limited and time consuming than the Wittig reaction, since metallated silicon derivatives are difficult to synthesize and their reactions are rarely stereoselective (T.H. Chan, 1974 ... 

If a Michael reaction uses an unsymmetrical ketone with two CH-groups of similar acidity, the enol or enolate is first prepared in pure form (p. llff.). To avoid equilibration one has to work at low temperatures. The reaction may then become slow, and it is advisable to further activate the carbon-carbon double bond. This may be achieved by the introduction of an extra electron-withdrawing silyl substituent at C-2 of an a -synthon. Treatment of the Michael adduct with base removes the silicon, and may lead as well to an aldol addition (G. Stork, 1973, 1974 B R.K. Boeckman, Jr., 1974). 

The prefix sila- designates replacement of carbon by silicon in replacement nomenclature. Prefix names for radicals are formed analogously to those for the corresponding carbon-containing compounds. Thus silyl is used for SiH3—, silyene for —SiH2—, silylidyne for —SiH<, as well as trily, tetrayl, and so on for free valences(s) on ring structures. 

SAN copolymers in [ACRYLONITRILE POLYTffiRS - SURVEY AND SAN (STYRENE-ACRYLONITRME CO-POLYTffiRS)] (Vol 1) -silylating agents for [SILICON COMPOUNDS - SILYLATING AGENTS] (Vol 22)... 

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